Rcpp check if list has an element

Question

My program deals with clustering. Apart from dataset user has to specify some details concerning clusters. There are two ways to approach that: you specify number of clusters or prepare list of clusters' descriptions.

args <- list(dataset=points, K=5)
args <- list(dataset=points, clusters=list(
                             list(type="spherical",radius=4),
                             list(type="covariance",covMat=matrix)
                                          )

next you call proper function (my program) in R with args as the argument.

classification <- CEC(args)

I would like to prepare CEC like below

SEXP CEC(SEXP args) {
  Rcpp::List list(args);
  arma::mat dataset = Rcpp::as<arma::mat>(list["dataset"]);
  if(list.contains("K")) {
    //something
  } else if(list.contains("clusters")) {
    //something
  }
}

I cannot find any API for List or example how to do that. Moreover, I study headers of Rcpp but definition of List which is typedef Vector<VECSXP> List ; is hardly helpful.

Is there anything I can use instead of list.contains() ?

Answer 1

You are probably looking for the containsElementNamed method:

Rcpp::List list(args);
if( list.containsElementNamed("K") ){
    // something
} else {
    // something else
}

https://github.com/RcppCore/Rcpp/blob/master/inst/include/Rcpp/vector/Vector.h#L584